A thin, flexible plastic liner or the like is often employed in a shipping box or other container to increase the shelf life of foods or other perishable commodities or to prevent leakage or spillage of product from a sealed shipping container. Such plastic liners are often in bag form. Heretofore, such plastic liners were often manually placed in the container or manually placed on a mandrel which was then used to line the container. The liner can also be manually placed over the open end of the container to be lined and then the liner can be automatically forced into the container by drawing the lining into the container using vacuum, as shown in U.S. Pat. No. 4,052,931 to Morse et. al., or by blowing the liner into the container, as shown in U.S. Pat. No. 4,537,584 to Everman et. al. Some attempts have been made to automatically open the liner before placing the liner over the open end of a container by using vacuum assemblies as shown in U.S. Pat. No. 4,522,012 to Nelson, U.S. Pat. No. 4,083,293 to Goldstein, and U.S. Pat. No. 4,537,584 to Everman et. al. However, the use of such vacuum assemblies in a totally automated lining process has been problematical. Vacuum cup or vacuum bar assemblies do not provide a positive grasp on each side of the liner to enable the sides of the liner to be completely pulled apart. In addition, simply separating the sides of the bag at the open end thereof does not completely open the bag since the sides of the bag tend to cling together due to surface tension or other adhesion between the inner surfaces of the liner. If the liner is not completely opened before it is placed over the upstanding flaps of the container, the liner will tear. Attempts to break such surface tension or adhesion while using vacuum cups or bars to separate the sides of the liner have not been successful. Thus, the need exists for a means of achieving the effective and positive automated opening of an unsealed end of a thin, flexible plastic film liner and for a method of breaking any surface tension or adhesion between the inner surfaces of the liner prior to inserting such a liner into a container. The present invention solves these problems by providing a novel jaw assembly and automated bag opener which frictionally grasps and separates the sides of a bag-type liner at the open end and securely holds the liner while it is completely opened, for example, by blowing air into the open end.